"DNA damage caused by chemical and physical factors can lead to detrimental effects to the cell and must be corrected. One of the primary pathways to achieve this repair is nucleotide excision repair (NER). In NER, the DNA damage is first located, a stretch of bases harboring the lesion is removed, and the gap is filled by a DNA polymerase. The unique feature of NER is its ability to correct a wide spectrum of DNA modifications of different sizes and chemical structures.The aim of the project is to structurally and biochemically characterize protein complexes involved in NER pathways in bacteria and eukaryotes.In bacterial NER, a complex of UvrA and UvrB proteins locates the damage and verifies its presence. In the first part of the project we plan to determine the crystal and small-angle X-ray scattering (SAXS) structures of a UvrA-UvrB-DNA complex to elucidate the details of the mechanism of the first steps of bacterial NER.In eukaryotic NER, the 3′ incision is executed by XPG/Rad2 protein. Currently, no structural information is available for this protein. In the second part of the project, we plan to solve the crystal structures of XPG/Rad2 nuclease in apo form and in complex with the DNA substrate to elucidate the mechanism of the 3′ cut. We also plan to determine the structure of XPG/Rad2 in complex with the XPG/Rad2-binding domain from the p62 component of TFIIH, which will be an important building block for the determination of the architecture of the eukaryotic NER pre-incision complex.The third part of the project will elucidate the structure and mechanism of the Rad16-Rad7 yeast NER complex. It is implicated in numerous stages of NER, from damage detection to ubiquitination of other NER components. We plan to solve the crystal structures of the Rad16-Rad7 alone and in complexes with DNA or partner protein Abf1 to elucidate the mechanisms of various activities of Rad16-Rad7 and help design experiments that could test the in vivo function of this complex."